If you smoke you should list down the amount you actually spend. It is ridiculous to tell a smoker of 20 per day, that they are allowed £12 per week. Let creditors be the ultimate judge of whether this is allowable, not your IP.
Hi Jonathan - make a list of what you actually spend each month. Don't try to get your disosable income as low as possible, if you make sure you include all your actual spends, your DI will be whatever it is. Only then can you really see if an IVA is for you.